1. Field of the Invention
The invention relates to an improvement to installations for producing nonwoven fibrous webs, the cohesion of which is obtained by intermingling of fibres in the thickness of the said web by the action of small-diameter high-speed fluid jets, more particularly water jets.
2. Description of the Related Art
U.S. Pat. No. 3,906,130 relates to a perforated nonwoven. Moreover, in that document, oscillations are intended to promote the transverse deposition of the filaments and the formation of filament loops.
FIG. 5 of that document also shows that the members delivering the water jets (reference 36) intended for consolidating the web of filaments are placed on a non-oscillating conveyor 15 independent of the oscillating conveyor 1 on which the filaments are deposited. The inventor specifies that the items 33, 34 and 35 placed above the conveyor 1 are nozzles for impregnation with a caustic soda solution for a scouring treatment. This caustic soda treatment can in no way be likened to consolidation by water jets, in other words to hydraulic entanglement of fibres. This is usually carried out at pressures not exceeding 5 bar and by flat or conical jets.
Finally, no mention is made of the marks of the jets disappearing, which goes without saying since the members delivering the water jets for the purpose of consolidating the filaments by hydraulic entanglement are installed on a non-oscillating conveyor.
U.S. Pat. No. 4,252,590 relates to a process for forming a web of continuous filaments, the transverse properties of which are improved by a transverse movement of the support 3.
The above document explains that an increase in the transverse strength of the web is obtained if the support itself undergoes a transverse movement.
Nowhere in that document is it mentioned that water jets are used to produce hydraulic entanglement of the filaments, nor is any disappearance of the lines left by the water jets in the filament web.
U.S. Pat. No. 3,833,438 discloses a particular spinning system called “wet” spinning in which the extruded and coagulated filaments are received on a conveyor undergoing a transverse oscillatory movement.
It is clearly specified that, in FIG. 1, the references 29 and 30 correspond to impregnation systems for acid or basic chemical treatments, as is practiced on webs of filaments after the latter have been spun.
That document does not mention the use of water jets for producing hydraulic entanglement of the filaments, nor any disappearance of the lines left by the water jets in the web of filaments.
It was proposed long ago, as is apparent from U.S. Pat. No. 3,214,819 and U.S. Pat. No. 3,508,308, to produce nonwoven fabric webs in which the cohesion is provided by the interlacing of the elementary fibres, the interlacing being obtained by the action of pressurized water jets that act on the fibrous structure and allow some of the constituent fibres of the web to be reoriented in the direction of the thickness.
The water jets used to interlace the fibres leave visible impressions on the surface of the nonwovens.
It has already been envisaged, as is apparent from U.S. Pat. No. 3,493,462, to impress oscillations on the water jets in order to obtain nonwovens without marks and without visible features.
The vibrations transmitted to the hydraulic equipment induce premature ageing of the equipment and introduce hazards for the operators.